The use of films to control the levels of reflection and transmission of a window at different frequency ranges of light is well known in the art. For vehicle windows and many windows of buildings and residences, glare is reduced by controlling transmissivity and reflectivity within the visible light range of wavelengths (400 nm to 700 nm). For the same window applications, heat load may be reduced by partially blocking solar transmission in either or both of the visible portion of the solar spectrum or the near infrared portion (700 nm to 1200 nm).
One known sequence of films for providing solar control is described in U.S. Pat. No. 6,034,813 to Woodard et al., which is assigned to the assignee of the present invention. The solar control arrangement includes a Fabry-Perot interference filter and a gray metal layer on a flexible polyethylene terephthalate (PET) substrate that may be subsequently attached to a window using an adhesive. The Fabry-Perot interference filter provides solar heat load reduction by preferentially passing light at certain wavelengths and reflecting light at other wavelengths.
In addition to the optical considerations relevant to providing solar control through a window, structural considerations must be addressed. Regarding structural stability, reducing the susceptibility of the optical arrangement to cracking during fabrication, installation or long-term use is an important goal. Reducing other forms of “corrosion” is at least as significant. Hardcoat layers are often added to provide protection, as is described in the above-referenced Woodard et al. patent. However, a hardcoat layer does not protect against corrosion that occurs during the fabrication process and has limited effectiveness against corrosion that is induced from the edges of the optical arrangement.